Reduced terminal testing system

ABSTRACT

A semiconductor wafer having dice that include circuitry that is placed into a mode when the circuitry receives an alternating signal having certain characteristics. The alternating signal may be supplied from a system controller through a probe, probe pad, and conductive path on the wafer.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of application Ser. No. 09/638,276,filed Aug. 14, 2000, now U.S. Pat. No. 6,543,785, issued Mar. 18, 2003,which is a continuation of application Ser. No. 08/994,843, filed Dec.19, 1997, now U.S. Pat. No. 6,118,138, issued Sep. 12, 2000, which is adivisional of application Ser. No. 08/713,606, filed Sep. 13, 1996, nowU.S. Pat. No. 5,898,186, issued Apr. 27, 1999.

BACKGROUND OF THE INVENTION

Field of the Invention: The invention relates to a semiconductor wafermode controlling assembly and, more particularly, to such an assembly inwhich modes of circuitry of dice (ICs) on the wafer are controlledthrough alternating signals applied to the dice through probe pads onthe wafers. The invention also includes methods for constructing andoperating such wafers and the assembly.

State of the Art: Typically, finished integrated circuit chip assembliesinclude a die or dice attached to a lead frame and encapsulated with anencapsulant. Numerous expensive and time consuming steps are involved inproducing such chip assemblies. These steps may include the following:(1) forming dice on a wafer substrate, (2) testing the dice, (3) cuttingdice from the wafer, (4) connecting a die or dice to a lead frame, (5)encapsulating the die or dice, lead frame, connecting wires, and anyauxiliary circuitry, (6) performing burn-in and providing other stressesto the dice, and (7) testing the assembly.

Defects in a finished chip assembly can prevent it from operating asintended. In spite of painstaking attention to detail, defects may beintroduced at various levels of production. For example, manufacturingdefects in the die may cause a failure. It has been found, however, thatsome defects are manifest immediately, while other defects are manifestonly after the die has been operated for some period of time.

Reliability curves are used to express a hazard rate or instantaneousfailure rate h(t) over time t, and often have a “bath tub” shape. Thereliability curves for many, if not all, ICs are generally like thatshown in FIG. 1. The reliability curve in FIG. 1 may be divided intothree regions: (1) an infant mortality region, (2) a random failuresregion, and (3) a wearout region.

The infant mortality region begins at time to, which occurs uponcompletion of the manufacturing process and initial electrical test.Some ICs, of course, fail the initial electrical test. Inherentmanufacturing defects are generally expected in a small percentage ofICs, even though the ICs are functional at time to. Because of theseinherent manufacturing defects (that may be caused by contaminationand/or process variability), these ICs have shorter lifetimes than theremaining population. Typically known as ICs suffering “infantmortalities,” while the ICs may constitute a small fraction of the totalpopulation, they are the largest contributor to early-life failurerates.

Once ICs subject to infant mortality failure rates have been removedfrom the IC population, the remaining ICs have a very low and stablefield failure rate. The relatively flat, bottom portion of the bathtubcurve, referred to as the random failure region, represents stablefield-failure rates which occur after the IC failures due to infantmortalities have been removed and before IC wearout occurs.

Eventually, as wearout occurs, the failure rate of the ICs begins toincrease rapidly. However, the average lifetime of an IC is not clearlyunderstood, because most lab tests simulate only a few years of normalIC operation.

“Burn-in” refers to the process of accelerating failures that occurduring the infant mortality phase of component life in order to removethe inherently weaker ICs. The process has been regarded as critical forproduct reliability since the semiconductor industry began. There havebeen two basic types of burn-in. During the process known as “static”burn-in, temperatures are increased (or sometimes decreased) while onlysome of the pins on a test IC are biased. No data is written to the IC,nor is the IC exercised under stress during static burn-in. During“unmonitored dynamic” burn-in, temperatures are increased while the pinson the test IC are biased. The IC is cycled under stress, and datapatterns are written to the IC but not read. Hence, there is no way ofknowing whether the data written is retained by the cell.

In recent years, as memory systems have grown in complexity, the needfor more and more reliable components has escalated. This need has beenmet in two ways. First, manufacturing process technology has reached alevel of maturity and stability where inherent manufacturing defects,caused by contamination and process variation, have been reduced. As aresult, latent failures have been significantly reduced, resulting inlower field failure rates. Secondly, more sophisticated methods ofscreening infant mortalities have been developed. As IC manufacturingpractices have become more consistent, it has become clear that burn-insystems that simply provide stress stimuli in the form of hightemperature and VCC (power) to the IC under test may be inadequate intwo areas: (1) such burn-in systems cannot detect and screen infantmortality failure rates measured in small fractions of a percent; (2)such burn-in systems are unable to confirm random failure rates that areclaimed to be significantly lower than 100 FITs (i.e., fewer than 100failures per billion IC hours) at normal system operating conditions.

To address these issues, an “intelligent burn-in” approach can beutilized. The term “intelligent burn-in,” as used in this discussion,refers to the ability to combine functional, programmable testing withthe traditional burn-in cycling of the IC under test in the samechamber. Advantages to this approach include:

(1) The ability to identify when a failure occurs and, thereby, computeinfant mortality rates as a function of burn-in time. As a result, anoptimal burn-in time for each product family can be established.

(2) The ability to correlate burn-in failure rates with life test datatypically obtained by IC manufacturers to determine the field failurerates of their products.

(3) The ability to incorporate into the burn-in process certain teststraditionally performed using automatic test equipment (ATE) systems,thereby reducing costs.

Some ICs have internal test modes not accessible during normaloperation. These test modes may be invoked on ATE by applying a highvoltage to a single pin. The IC is then addressed in a manner so as tospecify the operating mode of interest. Operating modes such as datacompression, grounded substrate, and cell plate biasing can be enabled,thus allowing evaluation of IC sensitivities and help in isolatingpossible failure mechanisms.

The electrical characterization data gathered from these tests is usedto identify which part of the circuit appears to be malfunctioning, thepossible location(s) on the IC, and the probable type or nature of thedefect. To facilitate discussion and reporting, failures are oftenclassified according to their electrical characteristics, referred to asthe failure mode. Typical classification of these modes includes thefollowing: single cell defect, adjacent cell defect, row failure, columnfailure, address failure, open pin, supply leakage, pin leakage, standbycurrent leakage, and entire array failure (all dead cells).

In anticipation that some ICs will have defects, many ICs are designedwith redundancies. In such ICs, a defective section of the IC may beshut off and a redundant but properly operating section activated andused in place of the defective section. For example, typical integratedmemory circuits include arrays of memory cells arranged in rows andcolumns. In many such integrated memory arrays, several redundant rowsand columns are provided to be used as substitutes for defective rows orcolumns of memory. When a defective row or column is identified, ratherthan treating the entire array as defective, a redundant row or columnis substituted for the defective row or column. This substitution isperformed by assigning the address of the defective row or column to theredundant row or column such that, when an address signal correspondingto the defective row or column is received, the redundant row or columnis addressed instead.

To make substitution of the redundant row or column substantiallytransparent to a system employing the memory circuit, the memory circuitmay include an address detection circuit. The address detection circuitmonitors the row and column addresses and, when the address of adefective row or column is received, enables the redundant row or columninstead.

One type of address detection circuit is a fuse-bank address detectioncircuit. Fuse-bank address detection circuits employ a bank of senselines where each sense line corresponds to a bit of an address. Thesense lines are programmed by blowing fuses in the sense lines in apattern corresponding to the address of the defective row or column.Addresses are then detected by first applying a test voltage across thebank of sense lines. Then, bits of the address are applied to the senselines. If the pattern of blown fuses corresponds exactly to the patternof address bits, the sense lines all block current and the voltageacross the bank remains high. Otherwise, at least one sense lineconducts and the voltage falls. A high voltage thus indicates theprogrammed address has been detected. A low voltage indicates adifferent address has been applied.

Antifuses have been used in place of conventional fuses. Antifuses arecapacitive-type structures that, in their unblown states, form opencircuits. Antifuses may be “blown” by applying a high voltage across theantifuse. The high voltage causes the capacitive-type structure to breakdown, forming a conductive path through the antifuse. Various flashdevices may be used.

Typically, ICs have numerous contacts that provide interfaces betweenthe circuits within the die and the outside world. The contacts are usedfor bond pads to which bond wires are connected. The bond wires are alsoconnected to the lead frame. The contacts (bond pads) may be used forvarious signals including those for addressing, data (DQ), VCC (power),VSS (ground), and control. However, physically, the contacts areextremely small or tiny. As such, it is impractical and expensive toprovide direct connections between each of the contacts and probes usedin, for example, testing, stressing, or repairing the IC. Probe padsthat are much larger than die contacts have been placed on, for example,the edge of the wafer. However, the sheer volume of contacts limits thenumber of contacts to which probe pads may be practically connected.

If there is a defect in an IC, it is desirable to discover the defect asearly as possible in the manufacturing process for a finished chipassembly. In that case, if it is determined that the defect cannot berepaired, the time and expense of completing a chip assembly will not beexpended. Further, some repairs may be less expensive to repair at anearlier stage of production of the chip assembly.

Accordingly, it would be desirable to test, stress, and, if necessary,attempt to repair ICs while they are still on a wafer, rather than in apackaged chip assembly.

U.S. Pat. No. 5,504,369 to Dasse et al. describes an apparatus forperforming wafer level testing of integrated circuit dice. Burn-in isdescribed as being performed while the dice are still connected to thewafer. Conductors are connected between wafer contact pads and contacts(bonding pads) on dice. In a preferred embodiment, the conductors supplysix voltage signals: power supply high voltage level signal, datasignal, reset signal, clock signal, power supply memory programmingvoltage level signal, and ground voltage level signal. For the followingreasons, connecting six conductors to each die has a considerable effectin terms of wafer real estate and/or processing steps. There are a largenumber of dice on the wafer. Current requirements dictate using numerouswafer contact pads and conductors to supply signals to the dice.Included extra conductors for redundancies increase the number by atleast a factor of two. Further, the conductors are positioned on top ofthe dice and/or in the dicing lanes (streets or street area of thewafer). Placing all six conductors in the dicing lanes requires eitherstacking the conductors one on top of the other in a dicing lane, and/orwidening the dicing lane (which may reduce the number of dice of thewafer). Placing several conductors over the dice requires additionalprocessing steps. The processing steps may be further increased whereconductors run both vertically and horizontally.

Accordingly, there is a need for an assembly in which a variety ofsignals may be supplied to dice in wafer form through a small number ofcontacts and conductive paths.

SUMMARY OF THE INVENTION

The present invention relates to a semiconductor wafer having dice thatinclude circuitry that is placed into a mode when the circuitry receivesan alternating signal having certain characteristics. The alternatingsignal may be supplied from a system controller through a probe, probepad, and conductive path on the wafer. In a preferred embodiment, theconductive path simultaneously carries a VCC power signal and thealternating signal to the circuitry. However, the alternating signal maybe carried on a conductive path different from the one carrying the VCCsignal.

A great deal of information may be conveyed through the alternatingsignal, making other signals unnecessary in controlling, testing,stressing, and repairing dice on the wafer. For example, clockinginformation may be conveyed through the alternating signal. Thecircuitry may be placed in different modes in response to differentcharacteristics of the alternating signal.

The alternating signal and a VCC power signal are received through asingle contact on each die. There may be redundant contacts, conductivepaths, and probe pads.

The dice may include additional circuitry that produces a signalindicating a particular event (e.g., a test is completed) has occurred.A fuse may be blown at the occurrence of the event.

A semiconductor wafer mode controlling system includes a systemcontroller to control application of the alternating signals and othersignals to the dice on the wafer. The semiconductor wafer modecontrolling system may also control a probe positioning controllerincluding an array of probes that selectively brings the probes intocontact with the probe pads, whereby the alternating signal having thecertain characteristics is transmitted from the probe to the circuitrythrough the probe pad and conductive path and the circuitry of each ofthe dice is placed into the mode. Each die on the wafer may be identicalor there may be differences in the dice. Where there are differences,the system controller may supply alternating signals having differentcharacteristics as needed.

The circuitry in the dice includes a local oscillator. A localoscillator may be off the die and on the wafer or in the systemcontroller.

When the dice are cut from the wafers and packaged or otherwise used incommercial applications, the circuitry may continue to be enabled or maybe disabled before a chip assembly containing one or more such dice iscompleted.

A wafer according to the present invention may be used in connectionwith a wide variety of semiconductor devices including memories (e.g.,DRAM or SRAM), microprocessors, control circuits, and ASICs. The wafermay be used in computer systems and in a wide variety of otherelectronic devices.

The invention includes a method of constructing wafers and wafer modecontrolling systems that have the above described characteristics.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

While the specification concludes with claims particularly pointing outand distinctly claiming that which is regarded as the present invention,the advantages of this invention can be more readily ascertained fromthe following description of the invention when read in conjunction withthe accompanying drawings in which:

FIG. 1 shows a graphical representation of a reliability curve thatexpresses a hazard rate h(t) as function of time t.

FIG. 2A shows a schematic top view of a semiconductor wafer under oneembodiment of the present invention.

FIG. 2B shows a schematic top view of a semiconductor wafer underanother embodiment of the present invention.

FIG. 3 shows a more detailed representation of an example of circuitryin a die on a wafer of FIG. 2A.

FIG. 4A shows an exemplary graphical representation of alternatingsignals superimposed on a VCC signal as a function of time.

FIG. 4B shows an alternative exemplary graphical representation ofalternating signals as a function of time.

FIG. 5A shows a schematic representation of a system used in connectionwith blocking instructions in the alternating signal that instruct thedice to send an output signal from the dice to a probe pad.

FIG. 5B shows a schematic representation of buffers used in connectionwith blocking an output signal from the dice to a probe pad.

FIG. 6A shows an embodiment of a wafer mode controlling system.

FIG. 6B shows a schematic top view of an embodiment of a wafer modecontrolling system in which a chamber contains multiple wafers.

FIG. 7 shows a first alternative input circuit that may be used in a dieas part of the present invention.

FIG. 8A shows a signal received at the input contact of the circuit ofFIG. 7.

FIG. 8B shows a signal supplied at an output of a regulator in FIG. 7.

FIG. 8C shows a signal supplied at an output clock extractor in FIG. 7.

FIG. 9 shows a second alternative input circuit that may be used in adie as part of the present invention.

FIG. 10A shows a graphical representation of certain signals included inthe alternating signal received by the circuit of FIG. 9.

FIG. 10B shows signal levels above and below a V_(IH) and V_(IL) range.

FIG. 11 shows a third alternative input circuit in which a secondcontact carries a reference signal.

FIG. 12 is a graphical representation of the input and reference signalreceived by the circuit of FIG. 11.

FIG. 13 shows a fourth alternative input circuit including adifferential circuit.

FIG. 14 shows an example of ranges of input signals that may be suppliedto the circuit of FIG. 13.

FIG. 15 shows a fifth alternative input circuit including a detector.

FIG. 16 shows a sixth alternative input circuit that may receive a localoscillator reference signal.

FIG. 17 shows a schematic representation of a chip assembly under thepresent invention as part of a computer system.

FIG. 18 shows a schematic representation of a chip assembly under thepresent invention as part of an electronic device.

DETAILED DESCRIPTION OF THE INVENTION

A. Wafer Overview

Referring to FIG. 2A, a semiconductor wafer 10 includes a substrate 14onto which numerous dice are formed through etching, deposition, orother well known techniques. Since there are many dice on a wafer, forclarity of illustration, only dice 18A, 18B, 18C, 20A, 20B, 20C, 22A,22B, and 22C (collectively “dice 18-22”) are shown.

Probe pads 26, 28, 30, 32, 34, and 36 (collectively “probe pads 26-36”)are formed on substrate 14. Because the size of dice 18-22 isexaggerated with respect to the size of wafer 10 and probe pads 26-36,the optimal placement of probe pads 26-36 is not shown. However, probepads 26-36 should be positioned such that the total number of dice onwafer 10 is either not reduced at all or reduced only by a minimum dueto the presence of probe pads 26-36. Such placement may be along theedge of wafer 10 where there is unused space caused by the round shapeof wafer 10 and the non-round shape of the dice.

Conductive paths, which may be conductive traces, are connected betweenprobe pads 26-36 and contacts on dice 18-22. For example, a conductivepath 42, which includes branches 42A and 42B, is positioned betweenprobe pad 26 and a first contact on dice 18A-18C and 20A-20C. Aconductive path 46, which includes branches 46A and 46B, is positionedbetween probe pad 28 and a second contact on dice 18A-18C and 20A-20C. Aconductive path 48, which includes conductive path branches 48A and 48B,is positioned between probe pad 30 and a third contact on dice 18A-18Cand 20A-20C.

Further, a conductive path 52 is connected between probe pad 32 andparticular contacts on a first contact of dice 22A-22C. A conductivepath 54 is connected between probe pad 34 and a second contact of dice22A-22C. A conductive path 56 is connected between probe pad 36 and athird contact on dice 22A-22C.

The conductive paths may run between dice in dicing lanes or “streets”,or run over dice. (A conductive path may also run in a street and over adice.) For example, conductive paths 46B, 48B, and 52 run along a street60 between dice 20A-20C and dice 22A-22C. As an example of differentpossibilities, conductive path 54 runs over dice 22A-22C. An insulatingcoating, such as a borophosphosilicate glass (BPSG) coating, mayseparate a die from a conductive path. Further, to keep the streetsnarrow, conductive paths may be stacked on top of each other. A via orother connection may be made from a conductive path through the coatingto a contact on die 22A. Coatings may also be useful to the extentconductive paths overlap. An advantage of the present invention over theprior art is that the number of conductive paths is reduced, therebyreducing processing steps in insulating conductive paths from each otherand other components on the wafer and, if necessary, in removinginsulation.

As illustrated, probe pads 26, 28, and 30 are connected to two sets ofdice (i.e., 18A-18C and 20A-20C). Probe pads 32, 34, and 36, however,are connected to only one set of dice (i.e., 22A-22C). This differenceillustrates that the invention is not limited to a particular number ofdice being connected to a probe. In practice, the controlling softwaremay be simpler if each probe pad is connected to the same number ofdice, but that is not required. Further, the controlling software willbe simpler if each die on a wafer is identical. However, the inventionis not limited to the dice on a wafer being identical.

In FIG. 2A, conductive paths are shown running in only horizontaldirections. However, the conductive paths may run in both horizontal andvertical directions, although doing so may add additional processingsteps. The conductive paths may run in only the vertical direction.

FIG. 2B is an alternative embodiment, which is the same as FIG. 2Aexcept that all the dice on the wafer are connected to a single probepad 30 through conductive path 48, which in turn is connected toconductive path branches 48A, 48B, and 48C, etc. Probe pad 30 may beconnected to VSS. As still another alternative embodiment, substrate 14may be connected to VSS, eliminating another probe pad.

B. Die Circuitry and Alternating Signal Examples

FIG. 3 provides an example of circuitry in die 22A of wafer 10 of FIG.2A. FIG. 3 is schematic in that the components are not necessarily toscale or in the only relative position. Various other circuitry may alsobe employed in addition to or in place of the circuitry illustrated inFIG. 3.

Referring to FIG. 3, conductive path 52 connects probe pad 32 (near anedge 64 of wafer 10) to a contact or bond pad 70A on die 22A. Inordinary operation of die 22A, conductive path 52 and contact 70A carrya VCC signal to internal circuitry of die 22A. To control modes of thecircuitry of die 22A, an alternating signal may be appliedsimultaneously with the VCC signal to conductive path 52 and contact70A. The alternating signal may be a continuous or discontinuous digitalsignal, a continuous or discontinuous analog signal, or some combinationof them. The alternating signal may employ a modulation scheme, such asfrequency modulation (FM), amplitude modulation (AM), phase shift keyingmodulation (PSK), pulse width modulation (PWM), quadrature phase shiftkeying modulation (QPSK), and others. The alternating signal may beapplied to a contact other than the VCC contact. It is not necessarythat the alternating signal be applied to a conductive path that alsocarries another signal; however, doing so may reduce the number ofconductive paths, probe pads, and probes required. A contact 94A mayprovide a VSS signal between die 22A and probe pad 36.

Various examples of alternating signals are illustrated in FIGS. 4A and4B. Referring to FIG. 4A, an alternating signal 74 is superimposed on aVCC signal 76. As used herein, “superimposed” means there is a voltageoverlap between alternating signal 74 and VCC signal 76. Digitalcircuitry often includes input buffers (such as input buffer 86 in FIG.3) that, for example, block signals between voltages V_(IL) and V_(IH).In such a case, it is desirable for the alternating signal to be aboveor below the range of V_(IL) to V_(IH) so that the alternating signalwill be invisible to the buffers. Digital circuitry may also includeisolation circuitry (such as low electrostatic discharge (ESD) latchingcircuit 88 in FIG. 3) that blocks very high voltages, e.g., 13 volts.

To illustrate some possibilities, from time t0 to time t1, alternatingsignal 74 is a square wave signal having a frequency f1. From time t1 totime t2, alternating signal 74 has a frequency f2, which is greater thanf1. In practice, the number of cycles at a particular frequency may bemore or less than is shown in FIG. 4A. From time t2 to time t3,alternating signal 74 employs a frequency modulation scheme.

FIG. 4B shows an alternating signal 80 at voltages greater than V_(IH)and a sinusoidal alternating signal 82 at voltages less than V_(IL). Ofcourse, the present invention is not limited to dice that includecircuitry that blocks signals between V_(IH) and V_(IL).

Types of alternating signals include control alternating signals anddata alternating signals. A control alternating signal conveys controlinformation to circuitry. A clock signal may be an example of a controlalternating signal. A data alternating signal conveys data to be writteninto storage or operated upon. For example, a microprocessor may operateon a data that is written into a register by adding it to data writtenin another register. Some alternating signals include both a controlalternating signal and a data alternating signal, because they containboth control and data information.

Referring to FIG. 3, signals passing through input buffer 86 are appliedto a VCC power bus 92. VCC power bus 92 carries both the VCC signal andthe alternating signal(s). Except for those circuits designed to passthe alternating signals, circuits connected to VCC power bus 92 blockthe alternating signals.

In operation, demodulator 100 determines one or more characteristics ofthe alternating signal. Information is conveyed through the alternatingsignal to die 22A by the characteristics. The alternating signals mayhave various characteristics including, but not limited to, peak-to-peakamplitudes, average amplitudes, frequency, change in frequency, durationor number of cycles at a particular frequency or voltage, andrelationship between average or peak-to-peak voltage and VCC or zerovolts or ground. Data may be transmitted through high and low voltageswithin the peaks of a square wave. It is noted that the alternatingsignal does not have to be periodic, or if it is periodic, it does nothave to be over a large number of cycles. The characteristics of thealternating signal may change with time (e.g., FIG. 4A) to add furtherinformation to control die 22A.

A great deal of information may be provided into an alternating signal.For example, upon demodulation, an alternating signal may providecircuitry with control information and clocking information, as well aspass data to be written into memory or operated on.

Clock signals used in die 22A may be generated through at least thefollowing means: (1) the clock signals are generated completely insidedie 22A with no control from signals outside die 22A; (2) the clocksignals are generated inside die 22A, but under at least some controlfrom the alternating signal supplied from outside die 22A; (3) clockinformation is encoded in the alternating signal and then extracted fromthe alternating signal by demodulator 100; or (4) the clock signal isgenerated completely outside die 22A and supplied to die 22A through thealternating signal or some other signal. Depending on how it isimplemented, means (2) may be an example of means (3). Use of thealternating signal in originating or controlling a clock signal(s) canhelp synchronize dice to each other and external circuitry. Clocksignals may be used for timing tests and/or to provide general timingcontrol and information.

As an example of means (2), a clocking device 106 (which may be a localoscillator) may be controlled by a lock signal from demodulator 100based on clocking information from the alternating signal on conductivepath 52 and VCC power bus 92.

By providing an oscillation signal through conductive path 52 andcontact 70A, it is not necessary to use a dedicated contact and probepad for the clock signal. Accordingly, one less probe pad is needed. Ofcourse, another conductive path may be used to provide clock signals orinformation.

Under some embodiments of the invention, a contact is used to providedata between a die and a probe pad. For example, referring to FIG. 3, asignal may pass from contact 130A of die 22A to probe pad 34, and/orfrom probe pad 34 through contact 130A to die 22A. Contact 130A may be,but is not required to be, a DQ contact. Contact 130A may be a contactthat is used only while die 22A is on wafer 10, or it may continue to beused in ordinary operation of die 22A after it is packaged. Examples ofuses for contact 130A include the following. First, a signal fromcontact 130A may indicate information about the results of tests orother occurrences in die 22A to off-wafer circuitry through probe pad34. As an example, a fuse or antifuse may be activated upon completionof a test allowing a particular signal to pass through contact 130A toprobe pad 34. The fuse may be blown in response to completion of a testor other event, the occurrence of which may be read then or later. Thesignal to activate the fuse or antifuse may come from contact 70A or130A, or some other contact. A signal through contact 130A may be assimple as a single bit (e.g., indicating a test was positive), or moreextensive or complicated to provide diagnostic information. The signalfrom contact 130A may be a stream of data providing, for example, dataread from array 114 or some other component in die 22A. There may bemore than one contact, such as contact 130A, used to transmit or receivedata.

A potential problem in providing output signals to a probe pad frommultiple dice is contention on the conductive path to the probe pad. Onepossible solution is to have a different conductive path for each dieoutput signal.

A second solution is to have only one output conductive path shared byseveral dice, and to design the dice to not provide output signals tothe probe pad until being instructed to do so by the alternating signalon conductive path 52. The system controller (which may be off-wafer asdescribed below in connection with FIG. 6) may instruct each die inorder (e.g., first die 22A, then die 22B, then die 22C, etc.) to respondto a particular test. If a die had not responded after a certain periodof time, the system controller may assume the die was defective in someregard and instruct the next die to respond through its contact 130A.Referring to FIG. 5A, one way in which dice may be instructed in orderby the alternating signal is to place buffers 138A, 138B, 138C, etc. onconductive path 52. Just prior to the time at which the dice are torespond, the alternating signal may instruct each die to place itsrespective buffer in high impedance mode. For example, die 22A may placebuffer 138A in high impedance mode by sending a signal through conductor140A. Die 22B may place buffer 138B in high impedance mode by sending asignal through conductor 140B, etc. Then, upon sending a signal throughcontact 130A to conductive path 54, die 22A may take buffer 138A out ofhigh impedance mode by sending a signal through conductor 140A. Thealternating signal may then instruct die 22B to send a signal throughcontact 130B to conductive path 54. Buffers 138A-138C may have circuitryto respond to an override by the alternating signal. Such an overridemay be used if the system controller has not received a signal onconductor 54 after a certain amount of time.

Another way in which the dice may respond in order would be for each dieto have its own identification code. A particular die would respond whena code on the alternating signal matched the identification code on thedie. The codes may be placed on the dice through a photo process orthrough the alternating signal.

A third solution is to place buffers along conductive path 54 which areenabled by, for example, a signal on conductive path 54. For example,referring to FIG. 5B, a buffer 144B may be enabled by a signal fromcontact 130A or some other contact on die 22A, allowing the signal fromcontact 130B to pass through buffer 144B to probe pad 34. Then thesignal from contact 130B (or from some other contact on die 22B) mayenable buffer 144C. Depending on the design, a buffer 144A (not shown)between contact 130A and probe pad 34 would not be necessary.

In FIGS. 2 and 3, there are three probe pads connected to each die.There may be a greater or lesser number of probes connected to each die.There are numerous combinations of contacts on the dice to which theprobe pads may be connected through conductive paths. The following aresome of the possibilities:

No. of contacts Contacts on die One contact 1) VCC (ground may be madethrough the back of the wafer) Two contacts 1) VCC 2) Gnd Twocontacts 1) VCC (ground may be made through the back of the wafer) 2)Signal or test contact Three contacts 1) VCC 2) Gnd 3) Signal or testcontact Four contacts 1) VCC 2) Gnd 3) First signal or test contact 4)Second signal or test contact

Contacts may be any input or output pin including power, address, data,control, n/c (no connects), and ground contacts.

C. System Level Examples

FIG. 6A shows one embodiment of a wafer mode controlling system 160.Wafer 10 is supported by a support 162, which may be part of a vacuumhandler. A probe positioning controller 166 includes an array of probes170 (including probes 170A, 170B, . . . 170N) held by a probe support174. Probe positioning controller 166 may lower or raise probes 170 as agroup. Alternatively, individual ones of probes 170 may be lowered orraised by, for example, solenoids.

A system controller 180 controls probe positioning controller 166through a conductor(s) 182. System controller 180 also sends signals toand perhaps receives signals from one or more of probes 170 throughconductors 184. Logic 192 (which may include one or more microprocessorsand dedicated hardware) provides signals to and may receive signals fromconductors 182 and 184 through drivers/buffers 188. A signal generator194 may be used to create signals. Alternatively, logic 192 may generateall signals needed. In a preferred embodiment, the alternating signalsthat are conducted over conductive path 52 originate in systemcontroller 180. Signals may also be generated from circuitry on wafer10. Memory 196 may be used to store data used by logic 192 and perhapssignal generator 194. System controller 180 may include both digital andanalog circuitry and drivers/buffers 188.

Wafer 10 may be housed in a heating chamber 200 (such as a burn-inoven), which may be an autoclave. Heat may be generated by heat stripsplaced on, for example, support 162.

Referring to FIG. 6B, an embodiment of the invention includes heatingchamber 202, which accommodates more than one wafer (e.g., wafers 10A,10B, and 10C, 10D) at a time, which may be simultaneously tested, orotherwise controlled, by system controller 180. (The wafers may bestacked, one above the other.) One or more probe positioning controllers(which may be like controller 166) may be used in heating chamber 202.Whether or not a heating chamber is used, more than one wafer may besimultaneously controlled by system controller 180.

The relatively small number of probes needed to control the waferreduces the space required in heating chambers.

D. Modes

Die 22A may enter, modify, operate within, or exit certain modes basedon the characteristics of the alternating signal obtained throughdemodulator 100 and associated circuitry. Data may be transmittedthrough the alternating signal in a mode. The following are examples ofthe various modes within which die 22A may enter, modify, operatewithin, or exit in response to reception of information from thealternating signal:

1. Testing Modes

Referring back to FIG. 3, in various testing modes, die 22A may performself-tests to determine whether certain portions of die 22A performaccording to specification. These tests may include functional and/orparametric tests. Merely as an example, test circuit 110 may write datato locations in an array 114 and then read from the locations in array114 to determine if the data was properly stored. Errors may beidentified through error block 118 and logic block 122. Other componentsof die 22A (such as periphery 128) may be tested.

Test patterns and addressing information may be provided on thealternating signal on, for example, conductive path 52. For example, afirst portion of the alternating signal may specify a particular test tobe performed. A second portion of the alternating signal may provide thedata to be written and the addressing information. A third portion ofthe alternating signal may indicate the conclusion of the test mode, orinitiate another event such as a self-repair mode. Alternatively, testpatterns and other information can be stored in memory on die 22A, or ina chip on wafer 10.

As discussed above, data may be passed from contact 130A throughconductive path 54 to probe pad 32. Such data may indicate that a testwas successful or a test was not successful, or other diagnosticinformation.

2. Stressing Modes

As noted above, certain defects in a die will only appear after the diehas been operated over a period of time under various conditions. Theseconditions may be accelerated in a self-stressing mode. An alternatingsignal with certain characteristics may initiate and controlself-stressing.

3. Repair Modes

In various self-repair modes, die 22A may repair various componentsthrough, for example, activating redundant circuits. The self-repairmodes, including back-end repair, may be activated by differentalternating signals. An alternating signal on conductive path 52 mayindicate which fuse or antifuse should be activated. Because complicatedtests may be done while the die is on the wafer, repairs may be donebefore stressing including burn-in, prior to the completion ofstressing, or after stressing.

Time and resources are saved if a repair is made before burn-in or otherstressing. Time and resources are also saved if it is determined beforeburn-in or other stressing that a repair is not available.

E. Additional Examples, Explanations, and Variations

Various input circuits may be used in die 22A. Referring to FIG. 7, afirst alternative input circuit 210 for die 22A includes a regulator 214and a clock extractor 218. FIG. 8A shows an alternating signal (or aportion of one) received at contact 70A. FIG. 8B shows the regulatoroutput at a conductor 224. FIG. 8C shows a clock output at a conductor226.

Referring to FIG. 9, a second alternative input circuit 230 for die 22Aincludes a standard input buffer 234 in parallel with a data buffer 236.The alternating signal is received on a contact 70A (which may act as arow address strobe signal (RAS) contact pad). As an example, referringto FIG. 10A, the alternating signal includes signals in the low levelrange 248 or alternative low level range 252 at, for example, low orradio frequencies. The data input levels are invisible to standard inputbuffer 234 if above V_(IH) or below V_(IL). Referring to FIG. 10B, aninput signal 242 at contact 70A in unmodulated form within range 248 isreceived at a contact. Input buffer 234 passes VCC (or the RAS signal),and data buffer 236 passes the data-in signal.

Referring to FIG. 11, a third alternative input circuit 260 is similarto circuit 230 of FIG. 10, except that circuit 260 includes a secondcontact 262 that receives a reference level signal (shown in FIG. 12). Astandard buffer 264 passes VCC and a buffer 266 passes the data-insignal from the alternating signal. Using contact 262 to pass areference signal allows more information to be held off chip, but at acost of an extra probe pad and conductive path.

Referring to FIG. 13, a fourth alternative input circuit 270 in whichthe data from contact 70A and data from contact 272 is fed into adifferential buffer 274 such that a reference voltage is not needed.Buffers 276 and 278 produce individual control and/or data streams, asdoes differential buffer 274 through summing the signals at contacts 70Aand 272. Referring to FIG. 14, the input signal to contacts 70A and 272may be modulated with amplitude modulation (AM), frequency modulation(FM), pulse modulation (PM), or any other acceptable format at, forexample, low frequency or radio frequency.

Referring to FIG. 15, a fifth alternative input circuit 280 receives theVCC and data-in signals at contact 70A. A standard buffer 282 passesVCC. A demodulator 284 includes a filter 286 and a detector 288 thatextract the data-in signal, which is passed through buffer 290. Detector288 may be, for example, an FM/PM discriminator or an AM detector. Thedetector design will vary with the method of modulation selected.

Referring to FIG. 16, a sixth alternative input circuit 300 receives theVCC and data-in signal from contact 70A and a reference local oscillatorsignal on a contact 302. The VCC signal is passed by standard buffer304. A detector 308 provides the data-in signal to buffer 312 based onsignals from filters 314 and 316. Again, supply of the reference signalfrom off chip makes the detector design easier. However, a carrierfrequency local oscillator may be on or off the die.

Note that there is not necessarily any significance in providingdifferent reference numerals for contacts 262, 272, and 302. Forsimplicity, the input circuits of FIGS. 7, 9, 11, 13, 15, and 16 do notnecessarily include all well known circuitry.

There are various data formats of the alternating signal. An exemplaryformat may include a header, data packet, addressing, or a parity bit.Supplying an external clock via an additional contact tends to greatlysimplify the circuit design.

The present invention may be used in connection with supervoltage testmeans and miscellaneous programming.

It is expected that the greatest utility for the present invention willbe for dice at the wafer stage. In most cases, it is expected that thealternating signal will not be applied to a die after it is packaged andused in ordinary operation. However, the alternating signal may beapplied and the die placed in modes or data communicated to the dieafter the die has been packaged and used in ordinary operation.Alternatively, the circuitry that responds to the alternating signalsmay be disabled prior to shipping the die for commercial use.

In any event, a chip assembly having a die constructed according to thepresent invention may be used in a computer system or other system. Forexample, FIG. 17 illustrates a computer system 320 that includes acomputer chassis 324, a keyboard 326, and a display monitor 328.Computer chassis 324 includes various electronic components including atleast one chip assembly 330. Chip assembly 330 includes a dieconstructed according to the present invention (i.e., a chip assemblythat includes a die having circuitry designed to receive an alternatingsignal). Once packaged, or otherwise prepared for commercial use, die22A would be part of such a chip assembly.

FIG. 18 illustrates an electronic device 340 that includes variouselectronic components including a chip assembly 344 (which may be thesame as chip assembly 330). Chip assembly 344 includes a die constructedaccording to the present invention. Electronic device 340 may be anyelectronic device that includes dice, including, without limitation,memory devices, printers, displays, keyboards, computers (such ascomputer system 320), oscilloscopes, medical diagnostic equipment, andautomobile control systems, to name only a few.

Substrate 14 may be formed of a variety of materials including siliconand gallium-arsenide. Wafer 10 is not limited to any particular shape orsize, although currently 6″and 8″ diameter wafers are popular. The diceare not limited to any particular type of dice. For example, the dicemay be formed of various materials including silicon andgallium-arsenide. The dice may be such as are used with any of variousmemory chips, microprocessors, or application specific integratedcircuits (ASICs).

Factors to consider in determining the number of probe pads includelimits to the amount of current passing through a single pad, expense,space available for probe pads, and avoiding complexity.

As used in the claims, the terms “connect,” “connectable,” or“connected” are not necessarily limited to a direct connection. Forexample, probe pad 32 is connected to die 22A, although indirectlythrough conductive path 52. Further, there may be intermediatedelectronic components along or in the conductive paths, for example,buffers or amplifiers. In such a case, probe pad 32 would still beconnected to die 22A, although indirectly. However, as used herein, theword “connected” refers to an operational connection and not a mereindirect connection. For example, every portion of the wafer is directlyor indirectly connected with every other portion, but not every portionis operationally connected to another portion.

The materials mentioned herein, such as probe pads, contacts, conductivepaths, and portions of the die and system, may be constructed accordingto various well known techniques from various well known materials.

There may be various standard, well known circuits on the wafer 10,other than the dice. Also, there may be additional buffers or amplifierson wafer 10 separate from the dice. Further, there may be reductantprobe pads, conductive paths, and contacts under the design of thepresent invention.

Having thus described in detail preferred embodiments of the presentinvention, it is to be understood that the invention defined by theappended claims is not to be limited by particular details set forth inthe above description as many apparent variations thereof are possiblewithout departing from the spirit or scope thereof.

What is claimed is:
 1. A method of testing for a semiconductor die,comprising: providing a semiconductor die having a bond pad havingcircuitry connected thereto on a substrate; providing a power signalhaving an alternating signal having a predetermined characteristicsuperimposed thereon to the semiconductor die using the bond pad;subjecting the semiconductor die to the alternating signal having thepredetermined characteristic superimposed on the power signal; andplacing the semiconductor die into a mode when the circuitry connectedthereto receives the alternating signal having the predeterminedcharacteristic.
 2. The method of claim 1, wherein the alternating signalcomprises a substantially continuous digital signal.
 3. The method ofclaim 1, wherein the alternating signal comprises a discontinuousdigital signal.
 4. The method of claim 1, wherein the alternating signalcomprises a continuous analog signal.
 5. The method of claim 1, whereinthe alternating signal comprises a discontinuous analog signal.
 6. Themethod of claim 1, wherein the alternating signal comprises a frequencymodulated signal.
 7. The method of claim 1, wherein the alternatingsignal comprises an amplitude modulated signal.
 8. The method of claim1, wherein the alternating signal comprises a phase shift keyingmodulated signal.
 9. The method of claim 1, wherein the alternatingsignal comprises a pulse width modulated signal.
 10. The method of claim1, wherein the alternating signal comprises a quadrature phase shiftkeying modulated signal.
 11. A method of testing for a semiconductor diecomprising: providing a semiconductor die having a bond pad havingcircuitry connected thereto on a substrate; and providing an alternatingsignal having a predetermined characteristic to the semiconductor diesuperimposed on a power signal using the bond pad of the semiconductordie; and placing the semiconductor die into a mode when the circuitryconnected thereto receives the alternating signal having thepredetermined characteristic, the alternating signal comprising at leastone of a continuous digital signal, a discontinuous digital signal, acontinuous analog signal, a discontinuous analog signal, a frequencymodulated signal, an amplitude modulated signal, a phase shift keyingmodulated signal, a pulse width modulated signal, and quadrature phaseshift keying modulated signal.